High Light Intensity and CO₂ Enrichment Synergistically Mitigated the Stress Caused by Low Salinity in Pyropia yezoensis

Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO2 (AC: 400 mu atm) and elevated CO2 (HC: 1000 mu atm)) under changing salinity (20, 30 psu) and light intensities (50, 100 mu mol photons m(-2) s(-1)) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO(2) levels could mitigate the stress caused by low salinity.